A curtain wall is an exterior building wall which carries no roof or floor loads. Principal elements of a curtain wall are wall panels, constructed of glass, metal, concrete, or a combination of several materials forming a composite fabrication into a single wall panel assembly. The wall panels are generally secured between horizontally and vertically extending mullions which are fastened to beams and columns of load bearing members arranged to form the structural frame of a building.
Curtain wall panel units and assemblies are generally prefabricated and manufactured to closely predictable sizes; however, beams and columns of the structural elements of the building to which the panel must be secured are much less precisely located at the erection site. Therefore, support members for connecting panels of the curtain wall to structural elements of the building must exhibit three predominating basic characteristics: load carrying capability to support the wall panel without substantial deformation, adjustability to facilitate attachment of panels to structural members, and sealing qualities to minimize infiltration of wind, rain, snow, hail, and the like.
Support members heretofore devised have not effectively incorporated the above predominating characteristics into a structure which could be rapidly assembled at the erection site for attachment of wall panels to form an enclosing envelope about the structural frame of the building.
Support structure heretofore devised has relied upon the internal strength of resilient gaskets having generally H-shaped cross-section, as described in U.S. Pat. No. 3,699,735, for providing structural strength for supporting the weight of wall panels as well as providing sealing capability. Variations of such H-shaped gaskets which employ filler strips of wedges insertable in grooves extending longitudinally of the seal member are illustrated in U.S. Pat. No. 2,655,239 and U.S. Pat. No. 3,138,229.
Resilient gaskets having slots formed in opposite sides thereof function effectively for providing seals along vertically disposed edges of panels and between horizontally disposed edges of panels and surfaces of mullions in specific installations wherein the mullion and panel lie in a common plane. However in installations in which a mullion, extending along the lower edge of the wall panel, is to support wall panels lying in a plane outwardly of the mullion, metallic structural members are generally attached to the outside of the resilient gasket and secured therethrough by bolts installed from exteriorly of the building, for example as disclosed in U.S. Pat. No. 3,766,698 and 3,488,906. Thus, the erection of appropriate scaffolding has been required heretofore for adjustment of support members attaching lower edges of panels to horizontally disposed mullions in instances wherein the wall panel and mullion lie in different vertical planes.
In addition to time consumed in installation of gaskets having metallic support members exposed to the exterior of the building, thermal insulating qualities of such support members is substantially less than that of support members having only non-metallic material exposed exteriorly of the building wall. It should also be noted that the metallic members exposed to the exterior of the building present corrosion and sealing problems and consequently more expensive maintenance than is required in installations wherein panel support members have only non-corrosive, non-conductive outer surfaces.